Three groups of Macaca irus (fascicularis) monkeys have been fed a diet containing 10% butter and 2% cholesterol for 7 1/2 months while one control group was fed a butter-and cholesterol-free control diet. After 2 weeks on the atherogenic diet the animals developed a hypercholesterolemia of 569 mg/100 ml (average) without hypertriglyceridemia; plasma LDL increased greater than 2 fold with no significant changes in VLDL and HDL; the lipoprotein electrophoresis was consistent with hyperlipoproteinemia type IIa. No further changes in blood chemistry were detected. No coronary atherosclerosis was detectable as yet by in vivo coronary angiography nor were signs of myocardial ischemia demonstrable by EKG. In previous pilot studies severe stenosing coronary atherosclerosis and ischemic myocardial changes were observed only after 12-18 months on the atherogenic diet. This baseline CAHD will be established in one group of animals after 18 months on this diet by serial in vivo coronary angiograms, serial EKG's serial blood chemistry determinations (including enzymes) as well as by correlating these in vivo findings with the post mortem pathology of the coronary arteries and myocardia. This baseline CAHD-group will serve as a reference point for the proposed subsequent studies on further progression (2nd group: 42 months atherogenic diet) and possible regression (3rd group: 18 months atherogenic diet, 24 months control diet) of the induced coronary atherosclerosis and CAHD.